The present invention relates to an excimer laser apparatus in which a rotary bearing of a laser gas circulating fan is supported by magnetic bearings.
FIG. 12 is a first example of a basic arrangement of an excimer laser apparatus to which the present invention can be applied. FIG. 13 shows an arrangement of a motor housing of the apparatus of FIG. 12. In the excimer laser apparatus, a laser gas is sealably contained in a laser container 1. The laser gas contains a halogen type gas, such as a fluorine gas. A pair of main discharge electrodes 2, 2 are disposed in the laser container 1 so as to obtain an electric discharge for performing laser beam oscillation. Further, a circulation fan 3 is disposed in the laser container 1, so as to generate a flow of laser gas having a high velocity between the main discharge electrodes 2, 2.
The circulation fan 3 has a rotary shaft 4 extending therethrough, which is projected beyond opposite end portions of the fan 3. The rotary shaft 4 is rotatably supported by radial magnetic bearings 7, 7, 7 without making contact therewith, that is, in a floating condition. A motor 9 is provided so as to operate the circulation fan 3.
A magnetic bearing generally includes, as basic elements, a rotor, stators made of electromagnets for effecting floating support of the rotor and position sensors for detecting the position of the rotor. The radial magnetic bearing 7 shown in FIGS. 12 and 13 comprises a rotor 7-3 (FIG. 13) provided on the rotary shaft 4, stators, i.e., electromagnets 7-1, 7-1 arranged in a spaced relationship around the rotor, and displacement detection sensors 7-2, 7-2 provided around a sensor target 7-4 on the rotary shaft so as to detect displacement of the rotary shaft 4. Displacement signals from the displacement detection sensors 7-2, 7-2 are input to a control circuit (not shown) for phase compensation and gain adjustment. Output from this control circuit is supplied to the electromagnets 7-1, 7-1, which generate a magnetic attraction force or a magnetic repellent force in accordance with this output, to thereby support the rotary shaft 4 so that it is floated at a predetermined position between the electromagnets 7-1, 7-1.
As mentioned above, the laser gas is a corrosive gas containing, for example, a fluorine gas. Therefore, the electromagnets 7-1, 7-1 providing the radial magnetic bearing are subject to a corrosive environment. As shown in FIG. 14a and FIG. 14b, the electromagnet (stator) 7-1 comprises a stator core (iron core) 7-1a and excitation coils 7-1b attached to the stator core 7-1a. A separation wall 14 comprising a non-magnetic body is provided on an inner circumferential surface of the electromagnet 7-1, which surface surrounds the magnetic bearing rotor 7-3 provided on the rotary shaft 4. This prevents the electromagnet 7-1 (especially the excitation coils 7-1b which are liable to corrosion) from making contact with the laser gas. In FIGS. 12, 13, 14a and 14b, reference numeral 6 denotes a motor housing; 8 a window through which a laser beam is emitted; 10 a protective bearing; 11 a gas inlet chamber; 12 a dust removing filter; 13 a gas inlet tube; and 15 a magnetic bearing frame.
When the separation wall 14 is provided on the inner circumferential surface of the electromagnet 7-1, a problem arises, such that a magnetic gap between the electromagnet 7-1 and the magnetic bearing rotor 7-3 becomes large, thus reducing a magnetic attraction force or a magnetic repellent force obtained for effecting floating support of the rotary shaft 4. Therefore, in order to obtain a desired magnetic force of the magnetic bearing for controlling floating support of the rotary shaft, it is required to increase the size of the electromagnet 7-1. This is also problematic because the magnetic bearing inevitably becomes large.
In view of the above, the present invention provides an excimer laser apparatus in which an excitation coil of an electromagnet of a magnetic bearing has corrosion resistance against a laser gas, thus reducing the size of the magnetic bearing while increasing the life of the magnetic bearing, and preventing contamination of the laser gas.
FIG. 15 shows a second example of a basic arrangement of an excimer laser apparatus to which the present invention can be applied. As shown in FIG. 15, in this excimer laser apparatus, a laser gas containing a halogen type gas, such as a fluorine gas, is sealably contained in a laser container 201. In the laser container 201, there are provided pre-ionization electrodes (not shown) for pre-ionizing the laser gas and a pair of main discharge electrodes 202, 202 for obtaining an electric discharge for performing laser beam oscillation. Further, a circulation fan 203 is provided in the laser container 201, so as to generate a flow of the laser gas having a high velocity between the main discharge electrodes 202, 202.
The circulation fan 203 has a rotary shaft 204 extending therethrough, which is projected beyond opposite end portions of the circulation fan 203. Radial magnetic bearings 206, 207 and an axial magnetic bearing 208 are provided at opposite ends of the laser container 201. The rotary shaft 204 is rotatably supported by these magnetic bearings 206, 207, 208 without making contact therewith, that is, in a floating condition. A motor 209 for operating the circulation fan 203 is provided on a shaft end side of the radial magnetic bearing 207.
Displacement sensor targets 206c, 207c, 208d and magnetic bearing rotors 206d, 207d, 208e of the magnetic bearings are secured to the rotary shaft 204. Further, a rotor 209b of the motor 209 is secured to the rotary shaft 204. Displacement sensors 206a, 207a, 208a, electromagnets (i.e., magnetic bearing stators) 206b, 207b, 208b, 208c and a stator 209a of the motor 209 are provided so as to face the displacement sensor targets 206c, 207c, 208d, the magnetic bearing rotors 206d, 207d, 208e and the rotor 209b of the motor 209, respectively.
Separation walls 210, 211 in the forms of thin-walled cylinders are provided on inner circumferential surfaces of the displacement sensors 206a, 207a and the electromagnets 206b, 207b of the radial magnetic bearings 206, 207 and the stator 209a of the motor 209. The separation walls 210, 211 are made of a material having corrosion resistance against a halogen type gas contained in a laser gas, for example, austenite type stainless steel such as SUS316L. Thus, the displacement sensors 206a, 207a, the electromagnets 206b, 207b and the stator 209a of the motor 209, which comprise cores (iron cores) and coil wires having poor corrosion resistance against the laser gas, do not make contact with the laser gas.
In the axial magnetic bearing 208, a separation wall 212 is provided so as to prevent the displacement sensor 208a from making contact with the laser gas, as in the case of the radial magnetic bearings 206, 207. With respect to the magnetic bearing stators of the axial magnetic bearing 208, that is, the electromagnets 208b, 208c, the stator cores are made of a ferromagnetic material having corrosion resistance against a halogen type gas contained in a laser gas, such as a permalloy. Therefore, only the excitation coils are protected by separation walls 213.
The displacement sensor targets 206c, 207c, 208d and the magnetic bearing rotors 206d, 207d, 208e of the magnetic bearings, which are secured to the rotary shaft 104, are disposed within a sealed space communicated with the laser container 101. Therefore, the displacement sensor targets 206c, 207c, 208d and the magnetic bearing rotors 206d, 207d, 208e are made of a ferromagnetic material having corrosion resistance against a halogen type gas, such as a permalloy. The rotor 209b of the motor 209 is made of a composite of silicon steel plates and an aluminum alloy, or a permanent magnet. Therefore, a separation wall 214 in the form of a thin-walled cylinder is provided on a surface of the rotor 209b, so as to prevent the rotor 209b from making contact with the laser gas.
However, in the above-mentioned arrangement in which the separation walls 210, 211 in the forms of thin-walled cylinders are provided on the inner circumferential surfaces of the electromagnets 206b, 207b of the radial magnetic bearings 206, 207, the magnetic gap between the electromagnets 206b, 207b and the magnetic bearing rotors 206d, 207d of the radial magnetic bearings 206, 207 is increased by a distance corresponding to the wall thickness of the separation walls 210, 211. This leads to low efficiency and an increase in size of the magnetic bearings.
Generally, a magnetic force of the magnetic bearing decreases in proportion to the square of a gap between the magnet and a target. Therefore, in order to maintain a desired magnetic force while the gap is increased two times, it is required to use a magnetic bearing in which the surface area of the electromagnet or the number of windings of the coil of the electromagnet is increased four times, or the magnitude of a control current applied to the coil is increased two times.
In view of the above, the present invention has been made. It is an object of the present invention to provide a long-life excimer laser apparatus in which deterioration of the laser gas in the laser container can be suppressed, and damage to the magnetic bearings caused by the laser gas can be suppressed.
It is another object of the present invention to provide an excimer laser apparatus in which the magnetic bearings can be reduced in size and operated efficiently, and which has a low power consumption.
The present invention provides an excimer laser apparatus comprising: a laser container in which a laser gas is sealably contained; a circulation fan which generates a flow of laser gas between main discharge electrodes; and magnetic bearings which support a rotary shaft of the circulation fan, wherein: each magnetic bearing comprises a magnetic bearing rotor provided on the rotary shaft and magnetic bearing stators provided around the magnetic bearing rotor; and each magnetic bearing stator comprises a stator core at least part of which is exposed toward the magnetic bearing rotor, coils being attached to the stator core, and an isolating member for isolating each coil from the laser gas. By this arrangement, the coils of the magnetic bearing are isolated from a corrosive atmosphere of the laser gas, so that corrosion of the coils can be prevented and the life of the magnetic bearing can be increased. Further, contamination of the laser gas which is caused by corrosion of the coils can be prevented. Therefore, product quality and reliability of the excimer laser can be improved. Because only the coil is protected by the isolating member and at least part of the stator core is exposed toward the magnetic bearing rotor, the magnetic gap between the stator core and the magnetic bearing rotor can be reduced. Therefore, the magnetic bearing can be reduced in size and operated highly efficiently. As a result, it is possible to provide an excimer laser which requires a small installation area and has a low power consumption.
In one embodiment of the present invention, the isolating member is made of a corrosion-resistant material having corrosion resistance against the laser gas and each coil is embedded in the isolating member made of the corrosion-resistant material.
In another embodiment of the present invention, the corrosion-resistant material is a ceramic or glass type hardened material.
In a further embodiment of the present invention, the isolating member comprises a coil case for sealingly enclosing each coil.
In a further embodiment of the present invention, the isolating member comprises a sheath covering each electrically conductive wire of which the coil is made.
In a further embodiment of the present invention, the stator core comprises a magnetic body which has corrosion resistance against the laser gas or a magnetic body which has been subjected to an anticorrosion treatment against the laser gas. By this arrangement, contamination of the laser gas due to corrosion of the stator core exposed to a corrosive atmosphere can be prevented.
In a further embodiment of the present invention, each magnetic bearing is a radial magnetic bearing; the stator core has projecting portions facing the magnetic bearing rotor; the coils are attached to the projecting portions; and at least part of each projecting portion extends through a separation wall and is exposed toward the magnetic bearing rotor, the separation wall comprising the isolating member. By this arrangement, the projecting portions extending through the separation wall comprising the isolating member can be disposed in proximity to the magnetic bearing rotor, thus reducing the magnetic gap between the stator core and the magnetic bearing rotor.
In a further embodiment of the present invention, the magnetic bearing stators comprise a plurality of rodlike projecting portions and a base portion to which the projecting portions are connected, the base portion having a ring-shaped cross-section. By this arrangement, electromagnets can be easily manufactured by first attaching the coils to the rodlike projecting portions and then connecting the projecting portions to the ring-shaped base portion.
In a further embodiment of the present invention, each magnetic bearing is a radial magnetic bearing; and the stator core has projecting portions facing the magnetic bearing rotor, the coils being attached to the projecting portions, and an end face member attached to a surface of each projecting portion facing the magnetic bearing rotor, the end face member comprising a magnetic body having corrosion resistance against the laser gas, the end face member being exposed toward the magnetic bearing rotor. By this arrangement, the end face member providing part of the stator core can be disposed in proximity to the magnetic bearing rotor, thus reducing the magnetic gap between the stator core and the magnetic bearing rotor.
In a further embodiment of the present invention, a plurality of U-shaped cores, each having two projecting portions formed therein, are provided as the stator cores; the coils are attached to each U-shaped core so that the two projecting portions form an N-pole and an S-pole; the plurality of U-shaped cores are provided around the magnetic bearing rotor so that each projecting portion faces the magnetic bearing rotor and that two adjacent projecting portions of two adjacent U-shaped cores have the same polarity; the end face member is provided so as to extend between and onto the projecting portions having the same polarity; and the isolating member is provided so as to extend between the projecting portions having different polarities, the isolating member comprising a non-magnetic body. By this arrangement, the coils of the magnetic bearing can be isolated from a corrosive atmosphere of the laser gas, by means of the end face members and the isolating member. On the other hand, the end face member providing part of the stator core can be disposed in proximity to the magnetic bearing rotor, thus reducing the magnetic gap between the stator core and the magnetic bearing rotor. Because the isolating member extending between the N-polar projecting portion and the S-polar projecting portion comprises a non-magnetic body, no magnetic short circuit is caused. A magnetic flux passes through the magnetic bearing rotor and effectively exerts a magnetic force.
In a further embodiment of the present invention, the stator cores comprise a ring-shaped base portion provided around the magnetic bearing rotor and projecting portions extending radially inward from an inner circumferential surface of the base portion, the projecting portions being arranged at substantially equal intervals in a circumferential direction of the base portion; the coils are attached to the projecting portions so that an order of arrangement of the projecting portions is such that the N-pole, the S-pole, the S-pole and the N-pole are repeated as a unit; the end face member is provided so as to extend between and onto the projecting portions having the same polarity; and the isolating member is provided so as to extend between the projecting portions having different polarities, the isolating member comprising a non-magnetic body. By this arrangement, as compared to the end face members being attached only to the surfaces of the projecting portions facing the magnetic bearing rotor, the number of the end face members used in the magnetic bearing can be reduced by half. Therefore, the number of connecting portions between the end face members and the isolating member can be reduced, and the separation wall comprising the end face members and the isolating member can be easily manufactured.